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Ceramic Biomaterials (Bioceramics)

Ceramic Biomaterials (Bioceramics). The class of ceramics used for repair and replacement of diseased and damaged parts of the musculoskeletal system are referred to as bioceramics . OBJECTIVES To examine chemical/physical properties of ceramics

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Ceramic Biomaterials (Bioceramics)

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  1. Ceramic Biomaterials (Bioceramics) • The class of ceramics used for repair and replacement of diseased and damaged parts of the musculoskeletal system are referred to as bioceramics. • OBJECTIVES • To examine chemical/physical properties of ceramics • To introduce the use of ceramics as biomaterials • To explore concepts and mechanisms of bioactivity

  2. Ceramics • (keramikos- pottery in Greek) • Ceramics are refractory polycrystalline compounds • Usually inorganic • Highly inert • Hard and brittle • High compressive strength • Generally good electric and thermal insulators • Good aesthetic appearance • Applications: • orthopaedic implants • dental applications • compromise of non-load bearing for bioactivity

  3. Types of Bioceramics

  4. Mechanical Properties

  5. Natural hard tissues are “ceramic”-polymer composites: Bones, Teeth, Shells Tissue = organic polymer fibers + mineral + living cells Mineral component (Ceramic) Bone: hydroxyapatite (HA) – Ca5(PO4)3OH Mineralization under biological conditions: Many elemental substitutions Protein directed crystallization Unique characteristics – crystal morphology and solubility Synthetic calcium phosphates are used as biomaterials – “bioactive” Nature’s Ceramic Composites Synthetic HA Bone HA

  6. Bioactivity vs. Biocompatibility • Biocompatibility : • Objective is to minimize inflammatory responses and toxic effects • Bioactivity - Evolving concept: • The characteristic that allows the material to form a bond with living tissue (Hench, 1971) • The ability of a material to stimulate healing and trick the tissue system into responding as if it were a natural tissue (Hench 2002). • Advantages: Bone tissue – implant interface, enhanced healing response, extends implant life • Biodegradability: • Breakdown of implant due to chemical or cellular actions • If timed to rate of tissue healing transforms implant to scaffold for tissue regeneration • Negates issues of stress shielding, implant loosening, long term stability

  7. Inert Ceramics: Alumina • History: • since early seventies more than 2.5 million femoral heads implanted worldwide. • alumina-on-alumina implants have been FDA monitored • over 3000 implants have been successfully implemented since 1987 Smaller the grain size and porosity, higher the strength • E = 380 GPa (stress shielding may be a problem) High hardness: • Low friction • Low wear • Corrosion resistance Friction: surface finish of <0.02 um Wear: no wear particles generated – biocompatible

  8. Inert Ceramics: Aluminum Oxides (Alumina – Al2O3) • Applications • orthopaedics: • femoral head • bone screws and plates • porous coatings for femoral stems • porous spacers (specifically in revision surgery) • knee prosthesis • dental: crowns and bridges

  9. Alumina Bioinertness • Results in biocompatibility – low immune response • Disadvantage: • Minimal bone ingrowth • Non-adherent fibrous membrane • Interfacial failure and loss of implant can occur

  10. Bioactive Ceramics: Glass Ceramics • Glass: • an inorganic melt cooled to solid form without crystallization • an amorphous solid • Possesses short range atomic order  Brittle! • Glass-ceramic is a polycrystalline solid prepared by controlled crystallization of glass • Glass ceramics were the first biomaterials to display bioactivity (bone system): • Capable of direct chemical bonding with the host tissue • Stimulatory effects on bone-building cells

  11. Bioactive Ceramics: Glass Ceramics • Composition includes SiO2, CaO and Na2O • Bioactivity depends on the relative amounts of SiO2, CaO and Na2O • Cannot be used for load bearing applications • Ideal as bone cement filler and coating due to its biological activity

  12. SiO2 B C A D CaO Na2O Bioactive Ceramics: Glass ceramics A: Bonding within 30 days B: Nonbonding, reactivity too low C: Nonbonding, reactivity too high D: Bonding

  13. Calcium (Ortho) Phosphate • Structure resembles bone mineral; thus used for bone replacement • 7 different forms of PO4 based calcium phosphates exist - depend on Ca/P ratio, presence of water, pH, impurities and temperature

  14. Calcium Phosphate • Powders • Scaffolds • Coatings for implants – metals, heart valves to inhibit clotting • Self-Setting bone cement

  15. Calcium Phosphates • Uses • repair material for bone damaged trauma or disease • void filling after resection of bone tumors • repair and fusion of vertebrae • repair of herniated disks • repair of maxillofacial and dental defects • ocular implants • drug-delivery • coatings for metal implants, heart valves to inhibit clotting

  16. Excellent Moderate Low Why Use Bioceramics? • Advantages to Bioceramics: • Biological compatibility and activity • Less stress shielding • No disease transmission • Unlimited material supply • Disadvantage of Bioceramics: • Brittleness – not for load bearing applications

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